Friday, July 25, 2014

Many moons ago I sat
through a lecture on facial recognition.
The lecturer put on the screen a
selection of faces - all blonde ladies. There were 30 pictures and we had to study them for three minutes and say how many women there actually were. I
spotted an unusual eyebrow more than once…. 15 times in fact. Ahhhh! I thought,
there are only 16 ladies featured. 15 singletons but every second picture was
Miss Eyebrow. The lecturer was trying to catch me out.

Of course there were only two ladies…15 pictures of each.
Most of the students in our group answered between 15-30 different women. In
Holland, students on the same course got
it 100% correct. Because the ladies were a Dutch pop star and a Dutch
newsreader. So if you ‘recognise’ a face, you are more likely to …err…
recognise a face.

The moral of that story is that you should not be a career
criminal if you look like somebody famous.
Unless you bear a remarkable resemblance to another career criminal I
suppose.

Facial recognition is fraught with problems. We find it
difficult to verbalise specific facial features unless they are odd in some
way. It would be difficult to describe George Clooney

to a another person well enough for them to recognise who exactly you
were describing, but throw in a notable
feature like Owen Wilson’s nose,

Bruce Forsyth’s chin,

Prince Charles’ ears

and
it becomes easier. Stature, race, height and build are too generic for recognition.

But unfortunately for forensic purposes, most folk are
average. Which makes mathematical sense.

The photofit system invented in the 70’s was useful, but not
realistic. It suffered from weird horizontal
lines. It was difficult for the witness to specify a likeness as it relied heavily on single
feature recall while our brains use a more holistic system. As humans, we see
a face, not a set of eyes, a nose, mouth etc. We have no memory for those individual
features. And there was the obvious problem that there might be no match in
the photo fit system for the witness to
use. Does it actually possess Owen Wilson’s nose among its variations. The
system was only ever supposed to give a ‘type likeness’, never a recognisable
image of the specific features of the person concerned.

Here are some famous folk
by photofit. I managed to guess two correctly.

Answers below...

And I had a go at photofitting myself. I know my own face
reasonably well but it’s c**p isn’t it!

Another test? A composite picture that consists of the top half of
one famous face and the bottom of another. The brain struggles. So
automatically we cover top or bottom with our hand and immediately say

David Bowie and Harrison Ford

Angelina and Helena

Scarlett and Helen

Hugh and Meryl

Separated, we can hone in on a feature we recognise but our
brain can’t pull that recognisable feature out the composite.

Only the whole face is ever stored in our memories.

You can see it is still problematic – and that is with faces you
know well. How accurate would it be for a stranger’s face seen fleetingly, in an
emotionally charged situation?

Now there is a more advanced system. The computer gives
nine basic images… then hones and morphs the face as a whole, remodelling as
the witness says ‘image four is good’,
but eyes more like five. And the computer remodels with the witnesses
best guess. Even at that the witness was describing Dame Judy Dench. The system operator guessed
he was trying to describe Jo Brand.

Jo

Judy

Recognition we find easy, but recall is not.

2.5% of the population have prosopagnosia – face blindness,
including Brad Pitt seemingly. Does that mean I could tell him I was Angelina and he would believe me.

‘Monica’ has the condition. Her own daughter was standing in
front of her in a bus queue and she didn’t
recognise her at all, until she spoke,
and moved. Monica is drawn to
distinctive looking people. She is fine
meeting folk for the first time, but when she meets them again she has to rely
on them recognising her and saying hello to her.

But then we have contact bias. We recognise best the type of
faces that we see every day. Somebody who lives in a white society can
discriminate fine details of the ‘white face’ as a whole, but when confronted
with an Asian or Polynesian face – they will recognise only the racial features.

Some bloke who was nifty with a pen wrote this….

Your face, my thane, is as a book where men
May read strange matters. To beguile the time
Look like the time; bear welcome in your eye,
Your hand, your tongue: look like the innocent flower,
But be the serpent under’t.

5 comments:

Very interesting piece, Caro. Computer facial recognition is also a big deal these days. Often the issue is to recognize one of a relatively small group (1000) of acceptable (person authorized) or unacceptable (known terrorist) faces. One common technique is to use "eigenfaces" - sort of an average face and the variations from it in certain key directions. The directions are not necessarily determined by specific features, but rather by a minimal way of separating the faces. Maybe 25 such "eigenfaces" will be enough for the 1000 candidates.Your post suggests that humans may do something similar, but smarter of course. No computer would be able to deal with the combinations of faces you showed (unless it knew they were combinations.I'm wondering how well it would do on the photofit composites. Hmm, maybe an interesting student project...

Caro, this is fascinating. Goes very well with the previous post on unreliabity of eyewitnesses. I guessed only two: Patrick Stewart and John Cleese. If I ever have to identify a killer, I hope the bad guy has a dimple in his chin!

I agree with AA. I got Connery, Stewart, Nicholson, and Prince Charles right off. I'd argue that Atkinson and De Niro look more like Peter Lorre and Burt Lancaster, respectively (my original guesses of course), and that Al Pacino should only look so good. The only one I completely missed was John Cleese who I saw as Peter Sellers. That's very interesting, because of all the faces, the only person I knew very well on a personal basis was John Cleese!